1. Field of the Invention
The present invention relates to an injection molding method of low melting point metal material, injection molding device and box, and more particularly, is suitably applied to the case of injection molding the low melting point metal material that is the material of the box of the notebook personal computer (hereinafter referred to as notebook PC) for example.
2. Description of the Related Art
Heretofore, as shown in FIG. 1, the magnesium alloy of low melting point metal material has been commonly used for the body box 60 forming the outer part of a notebook PC 50. And by taking advantage of the feature of said magnesium alloy, the personal computer main body trimmed down to light weight and having increased hardness has been realized.
In the case of manufacturing such body box 60 of the notebook PC, by pouring the molten metal of magnesium alloy molten to the predetermined temperature at the predetermined injection rate into the predetermined shape injection molding space (hereinafter referred to as cavity) provided in the metal mold by using the injection molding device of hot chamber system, for example. And by taking out said injected molten metal from the metal mold after chilling and solidifying said injected molten metal as the molded goods, the box 60 having the same shape as the cavity can be manufactured.
Then, on the surface of thus manufactured box 60, the model name and logo marks are printed and mounted into the main body of the notebook PC and shipped as a merchandise.
However, since the model name and logo marks are displayed on the surface of the box 60 by printing, it was difficult to give the high quality impression and upscale quality feeling to the user by the box 60 of the notebook PC. Accordingly, in recent years it has been required to form the model name and logo marks with characters to be expressed with a slightly dented form with respect to the surface of the box 60 (hereinafter referred to as concave character).
As shown in FIG. 2, in the case of manufacturing a box equipped with concave characters (hereinafter referred to as box with concave characters) formed with the name of model type and logo mark using concave characters on the surface by using the hot chamber system injection molding device 1, a metal mold 11 having the shape wherein a cavity 2 formed by the left metal mold 3A and the right metal mold 3B corresponds to the box with concave characters will be used.
At this moment, the injection molding device 1 injects the molten metal of magnesium alloy molten to higher temperature than the metal mold 3 into the cavity 2 from the injection device 9. And after chilling and solidifying said injected molten metal, the right metal mold 3B is moved in the direction of an arrow C by the hydraulic cylinder 8 and the left metal mold 3A and the right metal mold 3B are separated and the molded goods is taken out from the cavity 2.
However, as shown in FIG. 3, the molten metal poured in the cavity 2 of the metal mold 3 reflects irregularly in the direction shown by an arrow at the convex part 4 provided corresponding to the concave characters to be formed on the surface of the box. And deviation occurs in the flow of molten metal poured into the cavity 2 and the molten metal does not flow constantly in the cavity 2, and thus the interference streaks occur on the surface of the box with concave characters after it is molded.
Moreover, in the injection molding device 1 of the hot chamber system, since the molten metal molten to higher temperature than the metal mold 3 is poured into the cavity 2 of the metal mold 3 heated to the predetermined temperature at the predetermined injection rate, the molten metal of high temperature runs against the convex part 4 severely.
Accordingly, in the injection molding device 1, the convex part 4 of the left metal mold 3A is further heated and deteriorated. Thus, the breakage occurs, such as the edge of the convex part 4 is chipped. Thus, in the box with the concave characters, after it is being molded by the injection molding device 1, an disadvantage occurs such as the contour of the concave character part becomes unclear due to the chipped edge of the convex part 4.
At the same time, in the injection molding device 1 of the hot chamber system, since the high temperature molten metal runs severely against the convex part 4 and said convex part 4 is further heated, the molten metal sticks onto the surface of the convex part 4 when cooling off the molten metal and solidifying this, and thus making the molded goods difficult to be taken out from the metal mold 3. And as a result, level difference occurs on the bottom surface of the concave character formed on the surface of the box with the concave characters.
Thus, in the conventional injection molding device 1, since such as interference streaks occur on the surface of the box with concave characters after being molded, disadvantages such as the contour of the concave character formed on the surface becomes unclear and the level difference occurs on the bottom surface, and the breakage such as chip occurs on the convex part 4 of the left metal mold 3A, it has been difficult to manufacture a large quantity of boxes with concave characters without defect, and this created a problem that yields of boxes with good quality were not good.
In view of the foregoing, an object of this invention is to provide an injection molding method of low melting point metal material capable of easily forming the desired shape concave design molding unit on the surface of the molded goods in the case of injection molding using the low melting point metal material, an injection molding device and a box provided with the concave design molding unit and having high quality.
The foregoing object and other objects of the invention have been achieved by the provision of an injection molding method of low melting point metal material, an injection molding device, and a box. In the injection molding method of low melting point metal material for injecting the molten metal formed of low melting point metal material into the injection molding cavity with the predetermined shape provided in the metal mold and after cooling off and solidifying the molten metal, taking out molded goods from the injection molding cavity; since the injection molding cavity is formed inside by the first metal mold unit and the second metal mold unit contacted, the metal mold having the trapezoidal shape convex design forming unit with the predetermined height on the metal mold inside surface of the first metal mold unit or the second metal mold unit forming the injection molding cavity is heated to the predetermined metal molding temperature, and the molten metal heated to the predetermined melting temperature is injected into the injection molding cavity in the metal mold heated, and after the injected molten metal is being cooled off and solidified, the molded goods is taken out from the injection molding cavity by separating the first metal mold unit and the second metal unit, the flow of the molten metal poured into the injection molding cavity would not be disturbed but can be poured in at a uniform rate because of the oblique side of the convex design forming unit having the trapezoidal shape. And thus, the concave design forming unit having clear contour corresponding to the convex design forming unit can be formed on the surface of the box easily.
Furthermore, according to the present invention, in the injection molding device for injecting the molten metal formed of low melting point metal material heated to the predetermined temperature into the injection molding cavity with the predetermined shape provided in the metal mold heated to the predetermined metal mold temperature and taking out the molded goods from the injection molding cavity after cooling off and solidifying the molten metal injected; since the metal mold forms an injection molding cavity inside by the first metal mold unit and the second metal mold unit contacted and the trapezoidal convex design molding unit with the predetermined height will be provided on the metal mold inside surface of the first metal mold unit or the second metal mold unit forming the injection molding cavity, the flow of molten metal poured into the injection molding cavity would not be disturbed because of the oblique side of the trapezoidal convex design molding unit and the molten metal can be poured into the cavity constantly and the concave design molding part having the clear contour corresponding to the convex design molding unit can be easily formed on the surface of the box.
Furthermore, according to the present invention, in the box for electronic equipment to be obtained by injecting the molten metal formed of low melting point metal material heated to the predetermined temperature into the injection molding cavity of the predetermined shape provided in the metal mold heated to the predetermined metal mold temperature at the predetermined injection speed, and after cooling off and solidifying the molten metal injected, for taking out the molded goods from the injection molding cavity, since the trapezoidal concave design forming unit having the oblique side tilted the predetermined angle to the virtual side normal to the surface towards the bottom side from the surface is provided, the static load strength and twisting strength will be increased and simultaneously, smooth touch and the feeling of high quality can be obtained by the oblique side having the trapezoidal tilted angle of the concave design forming unit.